Forest soil nutrition

and total counts) correlated negatively. The overall assessment of soil activity, the soil respiration, did not correlate with either. Significant correlations were found between the principal components of pH, CLPP, EAA, and culturable and total number of bacteria, while no correlations were found to soil respiration, loss on ignition and soil moisture content. The pH in the test system might make differences between bacterial communities more detectable. The functional characterization of the bacterial communities by the growth based CLPP correlated positively to the bacterial community function assayed by the EAA, which is independent of growth and, hence, more closely reflects the in situ activities.

Phosphorus (P) is one of the major constituents in energy metabolism and biosynthesis of nucleic acids and cell membranes with an important role in regulation of a number of enzymes. Soil phosphorous is an important macronutrient for plant growth. Phosphorus deficiency in soil is a major problem for agricultural production. Total soil P occurs in either organic or in organic form. Phytic acid as phytate (salts of phytic acid) is the major form of organic phosphorus in soil and it is not readily available to plants as a source of phosphorus because it either forms a complex with cations or adsorbs to various soil components. Phosphate solubilizing microorganisms are ubiquitous in soils and could play an important role in supplying P to plants. Microorganisms utilizing phytate are found in cultivated soils as well as in wetland, grassland and forest soils. Various fungi and bacteria (including plant growth promoting rhizobacteria) hydrolyze this organic form of phosphorus secreting phosphatases such as phytases and acidic/alkaline phosphatases. A large number of transgenic plants have been developed which were able to utilize sodium phytate as sole source of phosphorus. However, the recombinant phytases were similar to their wild type counterparts in terms of their properties. Increased phytase/phosphatase activity in transgenic plants may be an effective approach to promote their phytate-phosphorus utilization. The extracellular phytase activity of transgenic plant roots is a significant factor in the utilization of phosphorus from phytate. Furthermore, this indicated that an opportunity exists for using gene technology to improve the ability of plants to utilize accumulated forms of soil organic phosphorus. This review is focused on the role of phytases and phytase producing microbes in promoting the growth of different plants.

The spatial distributions of contaminant metals (Hg, Pb, Zn, Cd, Cu) and a metalloid (As) in vegetable plots and paddy fields located near a large scale Pb/Zn smelter in Hunan province, China, were investigated. Soil located 4 km from the smelter was severely contaminated, with maximum concentrations of Hg, Pb, Zn, Cd, Cu and As as high as 2.89, 1200, 3350, 41.1, 157 and 93 mg kg À1 , respectively. Concentrations of soil metal and As decreased with distance in the dominant wind direction. Single-factor assessment indicated pollution levels of Hg, Pb, Zn and Cd were most severe, while pollution levels for Cu and As were less severe. Results from a potential ecological risk assessment indicated high risk associated with the soil within a 4 km radius, with the contribution for each contaminant calculated as follows: Cd (70.0%), Hg (19.4%), Pb (4.8%), As (3.0%), Cu (1.7%) and Zn (1.1%). The forest soil in the nearby city park was also affected by the atmospheric depositions from smelting activities. Soil profiles demonstrated the pollutants were mostly accumulated in the upper 20 cm layer. Contamination of the topsoil with Hg, Pb, Zn, Cd, Cu and As indicated remediation should be considered.

Introduction The Oslofjord region in SE-Norway has been subject to steady glacio-isostatic uplift during the whole Holocene. The final retreat of the ice at the termination of the last glacial took place in this area between 13,900 (retreat from Hvaler ice-marginal ridge) and 11,500 years BP (retreat from Ski ice-marginal ridge). Since then, the area has been characterized by continuous

A study was carried out to determine the effects of organic, inorganic fertilizers and integrated soil fertility management and irrigation levels (1,000, 750 and 500 ml per planting station) on coffee growth. There were no significant differences (p [ 0.05) in girth, number of leaves and number of primaries due to the different soil fertility management options. Significant differences (p \ 0.05) due to soil nutrient sources were observed in coffee height where inorganic fertilizer treatment resulted in tallest coffee plants (47.4 cm) and integrated soil fertility having the shortest coffee trees (42.8 cm) after 1 year. The highest irrigation level of 1,000 ml had the tallest plants with thickest stems while the lowest level had the shortest and thinnest plants (p \ 0.05). No significant differences were observed in the number of leaves and number of primaries due to irrigation treatments. Results indicate that inorganic fertilizers are the most effective at high irrigation levels while organic manure performs better than inorganic fertilizers under low irrigation water levels.

Many physical, chemical, mineralogical, and biological soil properties can be affected by forest fires. The effects are chiefly a result of burn severity, which consists of peak temperatures and duration of the fire. Climate, vegetation, and topography of the burnt area control the resilience of the soil system; some fire-induced changes can even be permanent. Low to moderate severity fires, such as most of those prescribed in forest management, promote renovation of the dominant vegetation through elimination of undesired species and transient increase of pH and available nutrients. No irreversible ecosystem change occurs, but the enhancement of hydrophobicity can render the soil less able to soak up water and more prone to erosion. Severe fires, such as wildfires, generally have several negative effects on soil. They cause significant removal of organic matter, deterioration of both structure and porosity, considerable loss of nutrients through volatilisation, ash entrapment in smoke columns, leaching and erosion, and marked alteration of both quantity and specific composition of microbial and soil-dwelling invertebrate communities. However, despite common perceptions, if plants succeed in promptly recolonising the burnt area, the pre-fire level of most properties can be recovered and even enhanced. This work is a review of the up-to-date literature dealing with changes imposed by fires on properties of forest soils. Ecological implications of these changes are described.

Aun cuando la aplicación de fertilizantes en las plantaciones forestales es una práctica común en el manejo silvícola, la utilización de fertilizantes aún no está bien integrada en la silvicultura. La fertilización se utiliza como una consideración adicional, pero no como una práctica de manejo indispensable del manejo silvícola. Tanto es así, que cuando se decide bajar los costos de la producción forestal, invariablemente
se elimina el uso de fertilizantes antes que cualquier otra opción en las distintas prácticas de manejo.
Existen diferentes razones que explican por qué no se ha desarrollado un concepto de manejo nutricional de las plantaciones forestales. En primer lugar, no se ha desarrollado un sistema estructurado de los componentes, y de su funcionamiento, involucrados en la nutrición y fertilización de las plantaciones. En segundo lugar, los ensayos de dosis de fertilización requieren un gran esfuerzo experimental durante un período prolongado de tiempo (hasta la cosecha), para lograr resultados consistentes que permitan su evaluación económica.
Se ha acumulado una gran cantidad de información analítica sobre distintos aspectos parciales del manejo nutricional que son difíciles de utilizar en la toma de decisiones en la fertilización.
Recientemente, con el desarrollo de modelos simples y funcionales del crecimiento de las plantaciones, existe la posibilidad de incorporar submodelos nutricionales.
Hasta el momento, los intentos realizados han sido poco satisfactorios ya que no presentan un análisis profundo del sistema nutricional de las plantaciones forestales.
En el libro, los autores efectúan un análisis sistémico de los componentes del sistema nutricional de las plantaciones forestales y de su funcionamiento. Por otra parte, analizan la corrección racional de los déficit nutricionales a través de la fertilización.
En los capítulos 1, 2, 3 y 4 se presenta el efecto de las variables ecofisiológicas que generan las tasas potenciales de acumulación de biomasa y nutrientes en plantaciones de pinos y eucaliptos, en un determinado ecosistema. Mediante este análisis, es posible estimar las tasas de crecimiento y la demanda de N y P durante el desarrollo
de las plantaciones de pinos y eucaliptos.
Por otra parte, en los capítulos 5 y 6, se analiza la dinámica en los ciclos interno y externo de los nutrientes en los árboles y en el mantillo del suelo forestal. Los procesos de almacenaje y movilización de nutrientes están relacionados tanto con la demanda como con los nutrientes del suelo.
En los capítulos 7 y 8 se presenta el análisis del suministro de nutrientes del suelo en los diferentes ecosistemas y su vinculación con la demanda de nutrientes de los árboles. La racionalización de la técnica de fertilización, qué nutriente agregar, qué fuente de fertilizante aplicar, cuándo y cómo aplicar los fertilizantes, se describen en los capítulos 9 y 10.
A continuación, el capítulo 11 se centra en las variables que determinan la eficiencia de la fertilización y en las características de la respuesta a la fertilización en las plantaciones forestales, conocida la demanda, el suministro de nutrientes del suelo y la eficiencia de la fertilización.
La evaluación económica de una fertilización continuada que permita corregir el estado nutricional de las plantaciones durante todo su desarrollo, se analizan en el capítulo 12.
Finalmente, en el capítulo 13, se desarrolla el diagrama de flujo y la operación del modelo conceptual Rodal, que incluye un submodelo de crecimiento y un submodelo nutricional que resumen y sintetizan en su estructura y funcionamiento todo el análisis realizado en los capítulos anteriores. Para su validación, se requiere contar con ensayos de fertilización que se prolonguen hasta la cosecha de las plantaciones
con el objeto de permitir una evaluación económica.

Forty five soil samples were collected from the four pedons of the hill areas at Chittagong University based on the depth of soil horizon. Soil profiles on hill top were relatively well developed and belonged to Ultisols according to USDA soil Taxonomy. The profiles at the piedmont were relatively young soils and classified as Inceptisols and Entisols. The soils of all profiles were characterized by coarse texture (38% to 73%, sand fraction), high bulk density (1.15 to 1.32 Mg•m −3 ), low organic-C content (0.26% to 1.73%), acid soil reaction ( 2 H O pH varied from 4.44 to 5.52 and pH KCl from 3.57 to 4.90). Soils in all pedons were poor in exchangeable bases and base saturation. The CEC values ranged from 9.12 cmolc•kg −1 to 14.5 cmolc•kg −1 while ECEC varied from 1.96 to 4.78 cmolc•kg −1 . The exchangeable Al (aluminum) concentration ranged from 0.41 to 0.66 cmolc•kg −1 . Exchangeable acidity level ranged from 0.74 to 1.25 cmolc•kg −1 . Exchangeable Al and aluminum saturation increased with depth and their concentrations were below the toxic range for tree stands.

Simple tests of structural stability are needed for evaluating the ease with which soils slake and erode when in contact with water. In a laboratory study, we related the percolation stability (PS) of 22 Nigerian soils to land use, soil properties, structural stability indices and simulated rainfall erosion. All measurements were carried out with the 1±2 mm diameter air-dry aggregates. Land use in¯uenced PS more than the type of soil. Forest soils, bush fallows, mulched, minimally tilled plots and pasture lands had rapid PS (>250 ml/10 min) values, whereas mulched conventionally tilled plots, bare fallows and continuously cultivated plots from where residues were removed by burning had relatively slow to moderate PS values (34± 241 ml/10 min). The single most important soil property that correlated positively with PS is organic matter (OM) (r 0.55 * ) followed by total Fe Al (r 0.52 * ). The signi®cant inverse relationship (r À0.49 * ) between log (PS) and log (pH/OM) indicates a decrease in PS of these acidic, low-OM soils with increasing pH levels. The percent water-stable aggregate (WSA) >0.20 mm diameter, aggregated clay index (AC) and clay dispersion ratio (CDR) correlated weakly with PS. Conversely, the sealing index (SI) (i.e. the ratio of saturated hydraulic conductivity of an uncrusted to that of a crusted soil) had a strong, inverse relationship with PS (r À0.97 *** ). These relationships indicate that PS measures the slakability (and not dispersibility) of soils. The relationship between PS and erosion (E) was an exponential decay form, E 102 e À0.0043PS (r 2 0.98) and showed that high interrill erosion rates would be expected on soils with PS < 250 ml/10 min. The PS which is simple to measure, is, therefore, a good indicator of structural stability for assessing the potential of these soils to erode. #

High intensity forest fires in Mediterranean ecosystems probably have long-term effects on the organic matter (OM) of the forest soils. Therefore, we analyzed the quality and quantity of humic materials extracted from the A horizons (0-15 cm) of a fire-affected (FA) and a control fire-unaffected (FU) Dystric Cambisol from the Sierra de Aznalcóllar (Spain). 13 C and 15 N solid-state nuclear magnetic resonance (NMR) spectra of the samples from the FA and FU sites confirmed that aromatic and newly formed heterocyclic N-forms are important fireinduced products. Wildfire resulted in a doubling of organic C and N concentration in the A horizon (0-15 cm) of FA. Solid-state 13 C NMR spectroscopy revealed that all C compound classes were enriched, including O-and N-alkyl C, with the highest for aromatic C (enrichment factor: 2.9). This suggests that the inputs from charred biomass and black carbon particles incorporated into the A horizon contained considerable amounts of unburned or partly charred remains. This conclusion is supported by the identification of diagnostic lignin-derived pyrolysis products in the hydrofluoric acid (HF) treated soils by analytical pyrolysis gas chromatography mass spectrometry (Py-GC/MS). Most of the partially charred material in addition to slightly altered plant necromass accumulated in the NaOH insoluble fraction (RES). Although the yield of alkali soluble OM from site FA was higher than that from site FU, the qualitative fire-induced alterations in C composition were slight. This may indicate that within this fraction, the OM was derived mainly from slightly charred or unburned materials. Fire also changed the chemical composition of the N-fraction of all humic extracts. These accumulated as pyrrole-type N compounds, although amide N was found to be the dominant form. This suggests that not all peptide-structures of the necromass were transformed by the fire. It is also possible that those amides are part of the melanoidized compounds, known to be formed during thermal treatment of mixtures containing sugars and amino acids. The fact that pyrrole-type N forms were not detected in the solid-state 15 N NMR spectra of FU supports their pyrogenic origin. Apart from the importance of the alkali-insoluble fractions of wildfire-affected soils as a source of molecular descriptors of the thermal effect, pyrrole identified in soil organic matter (SOM) by means of solid-state 15 N NMR spectroscopy could be a molecular marker for the presence of pyromorphic humic material in the soil. q

Soil amendment with organic materials prior to aorestation as well as the use of mycorrhizal inoculation, are advisable practices in aorestation of semiarid areas. In this work, the eect of both organic amendment and mycorrhizal treatment on the microbial activity of a soil aorested with Aleppo pine (Pinus halepensis Miller) was studied. Labile carbon fractions (water soluble carbon and water soluble carbohydrates), microbiological parameters (microbial biomass carbon, basal respiration and metabolic quotient), and enzyme activities such as oxydoreductases (deshydrogenase and catalase activities) and hydrolases (urease, protease and phosphatase) were determined. All these parameters were found positively in¯uenced by organic amendment and mycorrhizal treatment of plant roots by inoculation of fungi or forest soil addition. The best result was obtained when mycorrhizal inoculation with fungi was supplemented by organic amendment. 7

A novel Gram-negative, catalase-and oxidase-positive, strictly aerobic, non spore-forming, rod-shaped bacterium, designated strain JSM 083058 T , was isolated from non-saline forest soil in Hunan Province, China. Growth occurred with 0-8% (w/v) NaCl (optimum, 0.5-3%) at pH 6.0-10.0 (optimum, pH 7.0) and at 5-35°C (optimum, 25-30°C). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain JSM 083058 T fell within the cluster comprising species of the genus Sphingomonas, clustering with Sphingomonas aestuarii K4 T , with which it shared highest 16S rRNA gene sequence similarity (99.2%). The chemotaxonomic properties of strain JSM 083058 T were consistent with those of the genus Sphingomonas. The predominant respiratory quinone was ubiquinone Q-10, and the major cellular fatty acids were summed feature 8 (C18:1x7c/ C18:1x6c), C16:0, summed feature 3 (C16:1x7c/ C16:1x6c) and C17:1x6c. The polar lipids consisted of diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol and sphingoglycolipid. The genomic DNA G?C content of strain JSM 083058 T was 65.5 mol%. The combination of phylogenetic analysis, DNA-DNA relatedness, phenotypic characteristics and chemotaxonomic data supported the view that strain JSM 083058 T represents a novel species of the genus Sphingomonas, for which the name Sphingomonas hunanensis sp. nov. is The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain JSM 083058 T is FJ527417.

''Close-to-nature forest stands'' are one central key in the project ''Future oriented Forest Management'' financially supported by the German Ministry for Science and Research (BMBF). The determination of ecological as well as economical consequences of mechanized harvesting procedures during the transformation from pure spruce stands to close-to-nature mixed forest stands is one part of the ''Southern Black Forest research cooperation''. Mechanical operations of several typical forest harvesting vehicles were analysed to examine the actual soil stresses and displacements in soil profiles and to reveal the changes in soil physical properties of the forest soils. Soil compaction stresses were determined by Stress State Transducer (SST) and displacement transducer system (DTS) at two depths: 20 and 40 cm. Complete harvesting and trunk logging processes accomplished during brief 9-min operations were observed at time resolutions of 20 readings per second. Maximum vertical stresses for all experiments always exceeded 200 kPa and at soil depths of 20 cm for some vehicles and sequences of harvesting operations approached !500 kPa. To evaluate the impacts of soil stresses on soil structure, internal soil strengths were determined by measuring precompression stresses. Precompression stress values of forest soils at the field sites ranged from 20 to 50 kPa at soil depths of 20 cm depth and from 25 to 60 kPa at soil depths of 40 cm, at a pore water pressure of À60 hPa. Data obtained for these measured soil stresses and their natural bearing capacities proved that sustainable wheeling is impossible, irrespective of the vehicle type and the working process. Re-occurring top and subsoil compaction, increases in precompression stress values in the various soil horizons, deep rut depths, vertical and horizontal soil displacements associated with shearing stresses, all affected the mechanical strengths of forest soils. In order to sustain naturally ''unwheeled'' soil areas with minimal compaction, it is recommended that smaller machines, having less mass, be used to complete forest harvesting in order to prevent or at least to maintain currently minimal-compacted forest soils. Additionally, if larger machines are required, permanent wheel and skid tracks must be established with the goal of their maximum usefulness for future forest operations. A first step towards accomplishing these permanent pathways requires comprehensive planning with the Federal State Baden-Württemberg. The new guideline for final opening with skid tracks (Landesforstverwaltung Baden-Württemberg, 2003) proposes a permanent skid track system with a width of 20-40 m.

In Ethiopia, plantation forestry for the purpose of soil conservation and wood production is established mainly on degraded mountain slopes. These forests with a rotation age of 12-34 years consist of mainly exotic tree species; and have great potential to provide maximum wood production and economic incentives at the age of 8-20 years. 15 N natural abundance in soils under a 25-year-old forest on Mt. Yegof has been used to determine if the short rotation forests result in significant inputs of N to soils and improve the degraded soils before harvest at the rotation age of 12-34 years. Since I have previously described the fractional contributions of the present forest vegetation to the build-up of soil organic matter (SOM) on Mt. Yegof, patterns of d 15 N and d 13 C values were compared to determine if shifts in soil 15 N are related to vegetation shifts by afforestation. On Mt. Yegof, soil d 15 N values were 0.9-3.9% in soil at 0-5 cm and >6% in soil at 30-50 cm. Plant d 15 N values ranged from À4.6 to À0.7%. Despite the negative d 15 N values of the vegetation cover, the high d 15 N values in the topsoil indicate that return of N to soils by litter-fall is minimal on Mt. Yegof and, hence, the present forests do not change very much the soil 15 N signals at the surface layer. At this site, the high d 13 C values throughout the soil profiles is clear evidence of a long phase of C 4 grass dominance or cultivation of C 4 crops along the entire elevation gradient. The slight shift towards lower d 15 N values in soil at 0-5 cm indicate only a trend of 15 N depleted SOM build-up through litter-fall from the present forest vegetation. This and previous studies show that the planted forests on Mt. Yegof did not result in significant changes in the inputs of C, N and SOM, and hence, cannot signify the improvement of degraded soil conditions during a 25-year forest growth. Thus, these forests made need a rotation period much longer than 25-year period to signify ecological rehabilitation and to establish a sustainable forest ecosystem with less N losses on the fairly steep slopes at Mt. Yegof. From the points of view of soil conservation and soil fertility management, it could be suggested that forest harvest at the time of maximum wood production may not necessary be considered if ecologically sustainable forests are to be managed on highly degraded mountain slopes in the Ethiopian highlands.

The long-term effect of compost treatment on soil microbial respiration, microbial biomass carbon (C mic ) and biomass nitrogen (N mic ), soil organic carbon (SOC), and soil total nitrogen (STN) was studied in six degraded forests, Lower Saxony, Germany. The study was conducted in mature beech (Fagus sylvatica L.), pine (Pinus sylvestris L.) and spruce (Picea abies Karst.) forests on silty soils at Solling and on sandy soils at Unterlu Èû. Mature compost from separately collected organic household waste was applied for soil amelioration at an amount of 6.3 kg m 22 on the soil surface. After 2 years, soil samples were taken from the control and compost plots and were separated into .2 and ,2 mm fractions of the O-horizon and into mineral soil intervals from 0±5, 5±10, and 10±20 cm depths. The original compost had a pH of 7.5, high inorganic salt content, low organic C content, narrow C-to-N ratio, and low microbial activity and biomass. Compost signi®cantly reduced the microbial respiration per mass unit in the O-horizons .2 mm by 17% and in the O-horizons ,2 mm by 25%. C mic and N mic decreased signi®cantly by 22 and 23% in the O-horizons ,2 mm and by 35 and 28% in the O-horizons .2 mm, respectively. Our estimates suggest that the reduction in microbial respiration and biomass in the O-horizons resulted partly from the mixture of compost and the Ohorizons. The average loss of 1.2 kg m 22 organic matter may have also contributed to the reduction in microbial biomass and respiration in the O-horizons of the compost plots. However, it is not clear whether the decomposition of the original organic matter in the O-horizons was increased by the compost application. In the mineral soils, the compost treatment caused signi®cant increases in microbial respiration, C mic and N mic by 14±21% at 0±5 cm and by 14±23% at 10±20 cm depth. Although not signi®cant, a similar trend was found for the 5±10 cm depth. Increased release of nutrients and dissolved organic matter (DOM) could have promoted microbial growth and activity in the mineral soils. The signi®cant increase in STN and the narrowing C-to-N ratio indicate that the investigated forest soils were not N-saturated. This ®eld study suggests that super®cial application of compost from separately collected organic household waste increase microbial activity and biomass in the mineral soil by release of nutrients from the O-horizon to the mineral soil. q

The attribution of nitrous oxide (N2O) emission to organic and inorganic N fertilizers requires understanding of how these inputs affect the two biological processes, i.e. denitrification and nitrification. Contradictory findings have been reported when the effects of organic and inorganic fertilizers on nitrous oxide emission were compared. Here we aimed to contribute to the understanding of such variation using 15N-labelling techniques. We determined the processes producing N2O, and tested the effects of soil moisture, N rates, and the availability of organic matter. In a pot experiment, we compared soil treated with biogas waste (BGW) and mineral ammonium sulphate (Min-N) applied at four rates under two soil moisture regimes. We also tested biogas waste, conventional cattle slurry and mineral N fertilizer in a grassland field experiment. During the first 37 days after application we observed N2O emissions of 5.6 kg N2O-N ha−1 from soils supplied with biogas waste at a rate of 360 kg N ha−1. Fluxes were ca. 5-fold higher at 85% than at 65% water holding capacity (WHC). The effects of fertilizer types and N rates on N2O emission were significant only when the soil moisture was high. Organic fertilizer treated soils showed much higher N2O emissions than those receiving mineral fertilizer in both, pot and field experiment. Over all the treatments the percentage of the applied N emitted as N2O was 2.56% in BGW but only 0.68% in Min-N. In the pot experiment isotope labelling indicated that 65–95% of the N2O was derived from denitrification for all fertilizer types. However, the ratio of denitrification/nitrification derived N2O was lower at 65% than at 85% WHC. We speculate that the application of organic matter in conjunction with ammonium nitrogen first leads to a decrease in denitrification-derived N2O emission compared with soil receiving mineral fertilizer. However, at later stages when denitrification becomes C-limited, higher N2O emissions are induced when the soil moisture is high. Copyright © 2009 John Wiley & Sons, Ltd.

In forest and conservation nurseries in the Pacific Northwest USA, seedling production can be limited by root diseases caused by fungi in the genera Fusarium Link:Fr., Cylindrocarpon Wollenw., Phytophthora de Barry, and Pythium Pringsh. Fusarium, Cylindrocarpon, and Pythium are the most ubiquitous, whereas incidence of Phytophthora is mostly associated with coastal bareroot nurseries. All of these root pathogens are encouraged by water saturated soils or media. Seedlings infected with Fusarium, Phytophthora, or Pythium often appear chlorotic or necrotic with extensive root decay. Cylindrocarpon often causes serious root decay without shoot symptoms. The best approach to mitigate losses from these diseases is to use a holistic integrated pest management program. This program should combine chemical controls with cultural practices, particularly those that increase soil permeability and drainage and reduce potential sources of inoculum, especially by disinfesting seeds and containers reused for crops. In general, we found that seedlings meeting nursery specifications for outplanting on forest soil (proper height, root collar diameter, healthy shoot color, lack of disease symptoms) but having these disease organisms on their root systems perform as well as non-infected seedlings.

Extensive forest areas were ameliorated by large-scale liming in the last years in order to prevent proceeding acidification and degradation of forest soils. The hitherto knowledge of liming effects on the function of forest soils still appears insufficient for an unambiguous evaluation. Sorption properties of soils and acidity are favourably affected by liming and the favourable effect is usually manifested in the layer of forest floor humus and in mineral soil within ten years. Reduction of soil acidity stimulates development of a bacterial component of microflora, soil edaphon, and good prerequisites are formed for a release of nutrients from soil organic matter. Improvement of some physical parameters of soils and negative effect of liming on the depth of rooting in spruce, availability of nutrients at some sites and in connection with mechanical soil preparation were also described. A key point of liming effect on forest soils is nitrogen dynamics. Mineralization of nitrogen is...

An experiment involving the addition of simulated acid rain to two Canadian Shield orthic humo-ferric podzolic forest soils was carried out in the field and in the laboratory. Soils were subjected to treatments of pH 5.7, 3.5, and 2.0 water containing added nitric and sulphuric acids in a 1:2 molar ratio. Pore-water concentrations of H+, [Formula: see text], [Formula: see text], [Formula: see text], and Cl− were monitored at depths of 15–60 cm for up to 2 years. Some of the laboratory columns were dismantled after 1 year and total soil N, S, soil pH, and S adsorption characteristics were measured. Half the columns were sterilized in an attempt to assess the relative importance of microbial processes. Considerable H+ buffering by the soils was indicated, with soil pH unchanged even under the most acidic treatment. Nitrate but not ammonium production was suppressed under highly acid treatment conditions in the laboratory, while in the field only small concentrations of both nitrogen s...

Potential nitrogen mineralization rate Community level physiological profiles a b s t r a c t Soil microbial communities are of crucial importance for the functioning of ecosystems developing in post-mining areas. The objective of this study was to compare the properties of microbial communities in mine soils reclaimed for forestry and in mine soils developing under vegetation from natural succession. Soil samples were taken from a degraded site prior to reclamation (MS), a site after 2 years of lupine cultivation (LUP), reclaimed postmining sites afforested with Scots pine (R6, R20, R28), post-mining sites with spontaneously developing pine forest stands (S6, S20, S27) and two natural pine forest stands (F30, F100).

In the mountainous areas of Eastern Spain, soils have been cultivated in terraced orchards for centuries, although in the last decades, almond orchards are being abandoned. For this study, we selected four locations in SE Spain, with a similar vegetation mosaic, constituting forest, almond tree orchards, and orchards abandoned between 10 to 15 years previous to sampling. The main objective was to investigate the effects of changes in land use from forest to agricultural and posterior land abandonment on various physical, chemical, and biochemical properties. In all locations, all properties showed the highest values in forest soils, excepting pH and some eco-physiological ratios which were lowest under this land use. Abandoned agricultural soils showed a slight recovery in some properties compared to agricultural soils, the biochemical properties being the most sensitive indicators in reflecting these changes. All these results indicate that after land abandonment, soil microorganisms are more active as a consequence of the increment in the vegetation cover, with higher inputs as litter and root exudates. Moreover, the stopping of tillage may also have favored the increments in microbial biomass and activity. Nonetheless, these values are still low compared to forest soils, reflecting that 10–15 years of abandonment is not long enough to achieve a significant recovery in soil properties under semi-arid Mediterranean conditions. The metabolic quotient (qCO2) showed no general pattern in all locations in terms of land use, suggesting that this ratio is not specific enough to be used as an indicator in ecosystem succession.

Two of the National Parks of the only Biosphere Reserve in the Caribbean Islands, the Jaragua–Bahoruco–Enriquillo reserve, occur mostly within the Pedernales province (Dominican Republic). In these National Parks, Jaragua and Bahoruco, almost every tropical forest ecosystem is represented, as are the land uses most common to the Dominican Republic. Despite soil being a key natural resource that needs to be considered in any sustainable development programme, the literature contains very little information on the soils of this region.In this study, we analysed 41 topsoil samples representing the main forest types and land uses of the province. The factors examined were fertility (OM, N, P, K) and heavy metal contents (Cu, Cr, Pb, Cd, Ni, Zn). Mean OM, N and total and available metal levels were almost invariably higher in the natural forest soils compared to those given over to human activities, especially cultivated soils. This difference suggests the uptake of metals by the crops and, to a lesser extent, by animals feeding on crop remains and grassland plants. This hypothesis is supported by high total and available metal contents, especially of Zn, Cu, Pb and, in smaller measure, of Cr recorded in the solid waste landfill of the city of Pedernales. It appears that the cutting down and burning practices of a nomad type of cultivation, as well as the pressures of intensive agriculture and livestock rearing have resulted in heavy metals bound to the soil's OM. We propose this is an important point to consider for the management of these lands.

The phylogeny of the genera Periconiella, Ramichloridium, Rhinocladiella and Veronaea was explored by means of partial sequences of the 28S (LSU) rRNA gene and the ITS region (ITS1, 5.8S rDNA and ITS2). Based on the LSU sequence data, ramichloridium-like species segregate into eight distinct clusters. These include the Capnodiales (Mycosphaerellaceae and Teratosphaeriaceae), the Chaetothyriales (Herpotrichiellaceae), the Pleosporales, and five ascomycete clades with uncertain affinities. The type species of Ramichloridium, R. apiculatum, together with R. musae, R. biverticillatum, R. cerophilum, R. verrucosum, R. pini, and three new species isolated from Strelitzia, Musa and forest soil, respectively, reside in the Capnodiales clade. The human-pathogenic species R. mackenziei and R. basitonum, together with R. fasciculatum and R. anceps, cluster with Rhinocladiella (type species: Rh. atrovirens, Herpotrichiellaceae, Chaetothyriales), and are allocated to this genus. Veronaea botryosa, the type species of the genus Veronaea, also resides in the Chaetothyriales clade, whereas Veronaea simplex clusters as a sister taxon to the Venturiaceae (Pleosporales), and is placed in a new genus, Veronaeopsis. Ramichloridium obovoideum clusters with Carpoligna pleurothecii (anamorph: Pleurothecium sp., Chaetosphaeriales), and a new combination is proposed in Pleurothecium. Other ramichloridium-like clades include R. subulatum and R. epichloës (incertae sedis, Sordariomycetes), for which a new genus, Radulidium is erected. Ramichloridium schulzeri and its varieties are placed in a new genus, Myrmecridium (incertae sedis, Sordariomycetes). The genus Pseudovirgaria (incertae sedis) is introduced to accommodate ramichloridium-like isolates occurring on various species of rust fungi. A veronaea-like isolate from Bertia moriformis with phylogenetic affinity to the Annulatascaceae (Sordariomycetidae) is placed in a new genus, Rhodoveronaea. Besides Ramichloridium, Periconiella is also polyphyletic. Thysanorea is introduced to accommodate Periconiella papuana (Herpotrichiellaceae), which is unrelated to the type species, P. velutina (Mycosphaerellaceae).

A root window-based, enzyme-imprinted, membrane system has been modified to enable visualization of the activities of hydrolytic enzymes (acid phosphatase, aminopeptidase, chitinase, and b-glucosidase) in situ in forest soils. The approach can be used to correlate the distribution of enzyme activity with visible features such as roots, mycorrhizas, or mycelial mats. In addition, it enables accurate spatial soil sampling for analysis of microbial communities associated with enzyme activities. The substrates are colorimetric conjugates of napthol, where color develops instantly in the field, or fluorimetric conjugates of 4-methylumbelliferone, whose fluorescent products are detected by a gel-documenting system. The method will allow important questions about the relationship between taxonomic and functional diversity of soil microorganisms to be addressed and identification of enzyme activity hot-spots in soil.

The impact of four coniferous tree species and their corresponding soil factors on N transformation rates and presence of ammonia-oxidising bacteria (AOB) was studied in an acid pine forest soil (Appelscha, The Netherlands). Pine soil had a relatively low net nitrification rate, while spruce, fir and larch soils showed high net nitrification rates. 16S rRNA and amoA sequences were only found in soils with high nitrification rates and belonged solely to Nitrosospira cluster 2. We conclude that tree species, possibly through their effects on soil C/N ratios, determines the presence of Nitrosospira cluster 2. Whenever AOB are present, however, the AOB community composition appears to be similar. q

A new actinomycetes isolate ERI-26 was recovered from Nilgiri forest soil of Western Ghats and screened for its antimicrobial activity against pathogenic bacteria and fungi. Cultural characteristics were assessed in different culture media and 16s rRNA pattern strongly suggested that this isolate belonged to Streptomyces. The morphological and physiological characters were recorded. ERI-26 exhibited resistance to streptomycin. ERI-26 had the ability to produce enzymes such as amylase, cellulase and catalase. Maximum biological activity was obtained on Modified Nutrient Glucose Agar (MNGA) medium. ERI-26 showed activity against bacteria such as Bacillus subtilis, Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis and fungi such as Candida albicans, Aspergillus niger and Aspergillus flavus. The antibacterial substances were extracted using methanol from MNGA medium in which ERI-26 had grown for six days at 28 8C. The antimicrobial activity was assessed using broth microdilution technique. The lowest Minimum Inhibitory Concentration of methanol fractions of ERI-26 against S. epidermidis was 375 mg/ml and against C. albicans was 500 mg/ml. # 2008 Elsevier Masson SAS. All rights reserved.

Soil is a complex mixture of mineral nutrients, organic matter, water, air and living organisms. The primary nutrients for plant growth are organic matter, nitrogen, phosphorus and potassium. In order to find the status of pH, organic matter (C), total nitrogen (N), available phosphorus (P) and available potassium (K) in forest soil, the study was conducted in Ghwangkhola Sapaude Babiyabhir Community Forest in Putali Bazaar Municipality-8, Syangja, Nepal. Soil parameters are analyzed through different standard methods followed worldwide by many soil scientists. Soil pH of sample in all three strata was slightly acidic and varies from 5.7 to 7.18. The carbon percentage was high and varies from 0.65% to 2.39%. The total nitrogen in soil was medium and varies from 0.09% to 0.12%. The concentration of available phosphorus in soil was high and varies from 73.71 kg/ha-93.23 kg/ha. The concentration of available potassium on soil was quiet low and varies from 2.54 kg/ha-4.23 kg/ha. Higher organic matter in the forest land indicate low activities of nitrogen losing process, which is due to the closed nutrient cycling and minimal disturbance in the natural forest system. So, addition of fertilizer rich in potassium and increasing pH is recommended to maintain potassium fertility and neutral pH in the forest soil.

Several aluminium toxicity indices were applied to acid soils developed from various parent materials (granodiorite, slate and limestone) and sustaining various tree species (Quercus robur, Pinus radiata and Eucalyptus nitens), in Galicia, NW Spain. Some indices are based on the composition of the soil solid or liquid phases and some on the composition of the leaf or root tissues. The base cation saturation of the exchange complex was used as an index based on the composition of the soil solid phase. The indices based on the soil solution composition were various cation species concentrations, including phytotoxic aluminium species, or concentration ratios. The concentrations of Al and Ca and the Ca/Al molar ratio were used as indices based on the leaf and root tissue compositions. The application of various indices led to different results. According to indices based on the soil solution or plant tissue compositions, the greatest problems are expected in soils developed from limestone or granodiorite and sustaining P. radiata; fewer problems are expected in soils developed from slate and sustaining Q. robur. On the contrary, the saturation of the exchange complex predicts the highest aluminium toxicity risk in soils developed from slate and sustaining Q. robur, and the lowest risk in soils sustaining E. nitens.

The influence of forest stand composition on soil was investigated by comparing the forest floor (FH) and upper mineral soil (0-20 cm) nutritional properties of jack pine and aspen stands on two soil types of contrasting fertility, a coarse-textured and a fine-textured deposit, in a replicated design. The studied tree species are pioneers that are found after major disturbances in the southern boreal forest of western Quebec and that differ in their nutrient requirements but not in their growth rate. Soil organic matter as well as total and available N, P, K, Ca, Mg contents were determined and the relationships with nutrient accumulation in tree biomass were studied. On both soil types a greater total and available nutrient accumulation in the forest floor layer was observed in aspen than in jack pine whereas such differences between stand types could not be detected in the mineral soil. Differences in FH nutrient content between stand types were larger on coarse deposits than on fine-textured soils. These results support the hypothesis that tree species with greater nutrient requirements cause an enrichment of the surface soil at least in the short term. The modulation of tree species effect by soil type was contrary to the pattern observed in other studies since a greater expression of this effect was observed on poorer soils. Differences in soil nutrient content were related to levels of organic matter accumulation.

The effect of the amendment with alginite, an organic rock originating from the biomass of fossilized unicellular algae, on microbial activity of forest soils was tested using a pot experiment. Five variants of soil-alginite mixtures were tested in three replicates with two forest soils: a loose sandy soil and a sandy loam. Gravimetric moisture closely correlated with the dose of alginite in both soils. Basal respiration and catalase activity increased with the dose of alginite in the sandy soil, but not in the sandy loam, where the highest response was observed at intermediate doses of alginite. The correlations of microbial activity parameters with moisture in the sandy soil were also much closer than in the sandy loam. The amendment with alginite was thus effective in improving some of the selected microbial activity indicators, but the optimum dose of alginite strongly depends on soil texture.

Mechanized harvesting procedures for typical forest vehicles were analysed to examine soil stresses and displacements occurring in soil profiles and to reveal changes in physical properties of forest soils. All field experiments were carried out under traffic lanes of standard forest vehicles in forest stands of the southern Black Forest. The soil stresses were determined using stress state transducers (SST) and displacement transducer systems (DTS) at depths of 20 and 40 cm. Complete harvesting and trunk-logging processes with a total time span of 9 min were observed. The maximum vertical stresses for all experiments exceeded 200 kPa; some experiments showed maximum vertical stresses up to 500 kPa or more at a depth of 20 cm. To evaluate the impact of soil stresses on soil structure, the internal soil strength was determined by predicting the precompression stress. Comparison of soil stress data with the natural bearing capacity of the natural forest soil proves that sustainable traffic is not possible, irrespective of the vehicle type and the working process. Topsoil and subsoil compaction, an increase in the precompression stresses, deep rutting and vertical as well as horizontal soil displacement associated with shearing effects took place and affected the mechanical strength and the physical properties of forest soils. Considering these results, heavy forest machinery has a severe impact on soil physical properties such as air, heat, water fluxes and rootability. In order to sustain the present undamaged soil condition, a change in harvest logistics and organisation is necessary. This can be achieved with a permanent skid-trail system which has already been designed to implement new guidelines in Baden-Wu¨rttemberg,

Conversion of the tropical forest to pasture results in changes in the quality and quantity of the soil organic matter (SOM) and other physical and chemical soil properties. Most studies concerning the carbon (C) cycle have focused on soil C stocks. However, little information is available on tropical soil respiration rates. The objectives of this paper are, firstly, to determine how conversion of a natural forest to a pasture and P fertilization affect (1) some soil properties and carbon and nutrient content, and (2) CO 2 and CH 4 exchanges at the soil -atmosphere interface. For such purposes, a forest-to-pasture chronosequence (pasture established in 1983, 1987, and 1994) was selected at the Fazenda Nova Vida in Rondonia. Soil sampling was done during the dry season (July 1996) and 6 months later during the rainy season (January 1997). Results show increased pH levels, exchangeable cations, and carbon stocks with the pasture installation. On the contrary, the level of available phosphorus decreased with the increasing age of the pastures, justifying the phosphorus fertilization practice. Regarding the CO 2 and CH 4 fluxes, we found that the forest and pasture soils had greater respiration (CO 2 release) rates during the wet season than during the dry season but no specific and significant relationships between the emission and the pasture age was found. Forest soil CH 4 consumption rates were three times lower during the wet season, whereas pasture soils showed a net emission of CH 4 even during the dry season. D

To understand the soil microbial activities and community structures in different forests in a sand-dune ecosystem, we conducted a study of 2 topographic conditions, upland and lowland, under a Casuarina forest. As well, in the lowland site, we compared forest soil microbial properties under 3 coastal forests (Casuarina, Hibiscus and mixed stand). The soil microbial biomass did not significantly differ between the upland and lowland Casuarina forest sites.

The decomposition rate of fresh plant litter may decrease from ca. 0.1% per day in fresh litter to 0.00001 per day or lower in more completely decomposed material. This is due to changes in its organic-matter quality as the recalcitrant chemical components become enriched in the material. The decrease in decomposability (substrate quality) is complex, involving both direct chemical changes in the substrate itself and the succession in micro-organisms able to compete for the substrate with a given chemical composition. The concept`substrate quality' varies among litter species, though.

the two forest types examined with abundant AM hosts. Specifically, nitrate addition led to BRSP decreases in SMBW and increases in SMRO forests. Changes in BRSP accounted for a small fraction of the changes in SOC; appearing to increase as a fraction of residual SOC consistent with the idea that GRSP are recalcitrant. BRSP remained unchanged at BOWO sites despite a significant increase in SOC at these sites. Our results point to the potential of proteins as contributors to differential, mycorrhizal type-specific responses to changes in soil carbon following N amendment.

Soil organic matter is known to contain a stable fraction with an old radiocarbon age. Size and stabilisation processes leading to the formation of this old soil carbon pool are still unclear. Our study aims to differentiate old organic matter from young and labile carbon compounds in two acid forest soils (dystric cambisol, haplic podzol). To identify such fractions soil samples were exposed to oxidation with Na 2 S 2 O 8 and to dissolution by hydrofluoric acid (HF). A negative correlation between 14 C activity and carbon release after dissolution of the mineral matrix by HF indicates a strong association of stabilised carbon compounds with the mineral phase. A negative correlation between the 14 C activity and the relative proportion of carbon resistant to oxidation by Na 2 S 2 O 8 shows that young carbon is removed preferentially by this treatment. The fraction remaining after oxidation represents a certain stabilised, long residence time carbon pool. This old fraction comprises between 1 and 30% of the total soil organic carbon in the surface horizons, but reaches up to 80% in the sub-surface horizons. Old OC is mainly stabilised by organo-mineral associations with clay minerals and/or iron oxides, whereas intercalation in clay minerals was not found to be important.

We studied stand structures and soil properties in an old-growth forest and two 30-yr-old second-growth stands. In the old-growth forest, the total density and basal area average 1566 trees >1.25 m height ha −1 and 46.73 m 2 ha −1. The dominant trees are Scutia buxifolia and Celtis tala. Using multivariate techniques we distinguished three stands: PS1, dominated by S. buxifolia, is 1000 m far from the river. Its soil is shallow and loamy. PS2 and PS3, codominated by S. buxifolia and C. tala, are over 1200 m distant from the river. There the soil is deeper and has thicker texture and higher phosphorus and calcium concentrations than the near-the-river forest soil. Scutia buxifolia shows reverse J-shaped size-distributions and has morphological features of stress-tolerant species. Celtis tala shows oscillating decay size-curves that suggest recruitment pulses related to small gaps and it has morphological features of competitive species. Celtis tala was selectively cut in the past in the second-growth stands SNRD and SRD. The stand SNRD, 1000 m far from the river, is dominated by S. buxifolia. The second species is Schinus polygamus which presents the bell-shaped size-structure of the pioneer species. SNRD does not differ from its old-growth counterpart PS1 in total tree density, basal area and tree branching. The stand SRD, over 1200 m distant from the river, is co-dominated by S. buxifolia and by C. tala trees regenerated from stumps. SRD does not differ from its old-growth counterparts PS2 and PS3 in total tree density and basal area. As to tree branching, it does not differ from PS3, but differs from PS2. All the stands are being invaded by the exotic tree Ligustrum lucidum. The differences between the old-growth stands seem to be related to the gradients of soil texture and nutrient concentrations raising edaphic stress towards the river. In SNRD, the stress, the stress-tolerance of S. buxifolia, and the aptitude of S. polygamus to recruit in disturbed habitats seem to have prevented the post-logging recruitment of C. tala. In SRD, C. tala regenerated possibly due to a better competitive performance in a more favorable site. Under protection the second-growth stands recovered the old-growth quantitative features. We recommend the restoration of the qualitative features and the control of L. lucidum.

In this special section of Biogeochemistry, we present results from a snow manipulation experiment in the northern hardwood forest ecosystem at the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire, U.S.A. Snow is important as an insulator of forest soils. Later development of snowpacks, as may occur in a warmer climate, may result in increases in soil freezing (i.e. colder soils in a warmer world) and could cause changes in fine root and microbial mortality, hydrologic and gaseous losses of nitrogen (N), and the acid-base status of drainage water. In our study, we kept soils snow free by shoveling until early February during the mild winters of 1997/1998 and 1998/1999. The treatment produced mild, but persistent soil freezing and induced surprisingly significant effects on root mortality, soil nitrate (NO − 3 ) levels and hydrologic fluxes of C, N and P. In this special section we present four papers addressing, (1) soil temperature and moisture response to our snow manipulation treatment Hardy et al.), (2) the response of fine root dynamics to treatment (Tierney et al.), (3) the response of soil inorganic N levels, in situ N mineralization and nitrification, denitrification and microbial biomass to the treatment (Groffman et al.) and (4) soil solution concentrations and fluxes of C, N and P (Fitzhugh et al.). In this introductory paper we: (1) review the literature on snow effects on forest biogeochemistry, (2) introduce our manipulation experiment and (3) summarize the results presented in the other papers in this issue.

This paper defines landscape-scale patterns in the character of natural organic matter (NOM) and tests for relationships to catchment soil, vegetation and topography. The drainage network of a boreal catchment, subcatchment size 0.12-78 km 2 , in Northern Sweden was sampled in August 2002 during a period of stable low water flow. The NOM was characterized with UV/Vis spectroscopy, fluorescence, XAD-8 fractionation (%humic substances), gel permeation chromatography (apparent molecular weight), and elemental composition (C:N). The largest spatial variation was found for C:N, absorbance ratio, and specific visible absorptivity. The lowest variation was in fluorescence index, %humic substances and molecular retention time. The variation in total organic carbon (TOC), iron and aluminium concentration was more than twice that of C:N. Between headwater and downstream sites no significant changes were distinguished in the NOM character. At stream reaches, junctions and lakes little change (<10%) in NOM character was observed. Common factor analysis and partial least squares regression (PLS) revealed that the spatial variation in surface coverage of lakes and mires could explain some of the variation of TOC and NOM character. Our suggestion is that the mosaic of landscape elements (different amounts of water from lakes, forest soil and mires) delivers NOM with varying characteristics to a channel network that mixes conservatively downstream, with possible small changes at some stream reaches, junctions and lakes.

The study was conducted on alluvial-meadow, maroon-forest soils and vertisols with Virginia tobacco. The total content of lead and cadmium is measured through decomposition by HF, HClO4, and HNO3 acids. A solution of 0.005 M diethylentriaminepentaacetic acid + 0.1 M triethanolamine, pH 7.3 was used for extraction of the elements’ mobile forms from soils. The preparation of plant samples was made by means of dry ashing and dissolution in 3 M HCl. An atomic absorption spectrometer “Spektra AA 220” of the Australian company Varian was used for determination of Pb and Cd content in the soil and plant samples. Certified reference materials (three soils and tobacco leaves) were also analyzed for the verification of the accuracy of Pb and Cd determination. A correlation/regression analysis was conducted between pH, humus content, total and mobile forms of lead and cadmium in the soil, and the concentration of these elements in the aboveground biomass of Virginia tobacco. It was established that there are no statistically significant dependencies determined between soil pH and lead concentration in the plant organs of Virginia tobacco. Regressional dependencies of great significance were determined between the humus content, total and mobile lead and cadmium in the soil, and the element concentration in the leaves of the three harvesting zones.

The effects of pyrogenic carbon on the microbial diversity of forest soils were examined by comparing two soil types, fire-impacted and non-impacted, that were incubated with laboratory-generated biochars. Molecular and culture-dependent analyses of the biochar-treated forest soils revealed shifts in the relative abundance and diversity of key taxa upon the addition of biochars, which were dependent on biochar and soil type. Specifically, there was an overall loss of microbial diversity in all soils treated with oak and grass-derived biochar as detected by automated ribosomal intergenic spacer analysis. Although the overall diversity decreased upon biochar amendments, there were increases in specific taxa during biochar-amended incubation. DNA sequencing of these taxa revealed an increase in the relative abundance of bacteria within the phyla Actinobacteria and Gemmatimonadetes in biochar-treated soils. Together, these results reveal a pronounced impact of pyrogenic carbon on soil microbial community composition and an enrichment of key taxa within the parent soil microbial community.

Soil organic carbon (C) is a complex set of pools, and to understand its dynamics it is necessary to know which of these pools are active at a given moment, and which act as passive, due to either physical protection or biochemical recalcitrance, or both. This matter has been studied mainly in agricultural soils. For forest soils, especially in Mediterranean areas, there is a data gap that needs to be filled. Therefore, we studied three profiles in Catalonia (NE Spain) over marl and under Pinus halepensis stands. Soil horizons were incubated under optimal conditions for 45 days. The respiration rate on day 45 was taken as basal respiration rate (BRR). The following fractions were quantified: (1) soluble C, (2) microbial C, both corrected (MCC) and uncorrected (MCUC) (i.e., applying or not a correction factor to account for the non-extractable microbial carbon), (3) C in size fractions, isolated by ultrasonic dispersion and sieving plus sedimentation, and (4) labile and recalcitrant C, quantified by acid hydrolysis, applied to both the whole soil horizons and the size fractions. The basal respiration rate (BRR) correlated best with the sum soluble + MCUC, which altogether seem the best estimator of the active C pool. The correlation between BRR and MCC was worse, thus suggesting that not all microbial C should be included in the active pool. The correlation of BRR with the C associated to coarse fractions (>50 µm) was positive, whereas that\with C associated to fine fractions (<20 µm) was negative. The correlations were lower than those obtained with the soluble + MCUC, thus suggesting that the coarse organic fractions are probably the main source of active C, but not active C itself. Alone, the pools obtained by acid hydrolysis (labile and recalcitrant) correlated poorly with BRR, but the combination of size fractionation with acid hydrolysis resulted in some of the best predictors of microbial activity. Hydrolyzable polyphenolic compounds inhibited microbial activity. Unhydrolyzable C associated to fine fractions (<20 µm) seemed the most stable of all the C pools studied. By contrast the unhydrolyzable part was apparently as unstable as the hydrolyzable part in the coarse organic debris. Overall, our results point to a hierarchy of constraints: both the physical protection and the biochemical quality affect microbial activity, but the physical protection goes first. In the profiles studied, C did not appear to be more stable in deep horizons than in surface horizons.

In Brazil, no tillage (NT) is a soil conservation practice now widely adopted by farmers, including smallholders. The effect of NT and conventional tillage (disc ploughing followed by two light disc harrowings, CT) was investigated on the aggregation properties of a clayey Rhodic Ferralsol from southern Brazil under different crop rotations. The same soil type under secondary forest was used as reference. Macro-and microaggregate classes were separated by wet sieving using a series of eight sieves (8, 4, 2, 1, 0.5, 0.25, 0.125, 0.053 mm) at four sampling layers (0-5, 5-10, 10-20, 20-30 cm). The soil in general had high structural stability. At 0-5 cm, meanweight diameter (MWD, 11.1 mm) and total organic C in macroaggregates (TOC, 39 g kg −1 soil) were highest for the forest soil. Soil under NT had a more similar distribution of aggregate size classes and TOC to the forest soil than CT. The most pronounced difference between tillage systems was observed in the surface soil layer (0-5 cm). In this layer, NT had higher aggregate stability (AS NT : 96%; AS CT : 89%), had higher values of aggregate size distribution (MWD NT : 7.9 mm, MWD CT : 4.3 mm), and had on average 28% greater TOC in all aggregate size classes than CT. Soil under NT had greater TOC in macroaggregates (NT: 22 g kg −1 ; CT: 13 g kg −1 ). Crop rotation did not have a significant effect on soil aggregate distribution and TOC. By increasing macroaggregation NT increased organic carbon accumulation in soil.

We report the rapid acidification of forest soils in the San Bernardino Mountains of southern California. After 30 years, soil to a depth of 25 cm has decreased from a pH (measured in 0.01 M CaCl 2) of 4.8 to 3.1. At the 50-cm depth, it has changed from a pH of 4.8 to 4.2. We attribute this rapid change in soil reactivity to very high rates of anthropogenic atmospheric nitrogen (N) added to the soil surface (72 kg ha-1 year-1) from wet, dry, and fog deposition under a Mediterranean climate. Our research suggests that a soil textural discontinuity, related to a buried ancient landsurface, contributes to this rapid acidification by controlling the spatial and temporal movement of precipitation into the landsurface. As a result, the depth to which dissolved anthropogenic N as nitrate (NO 3) is leached early in the winter wet season is limited to within the top ~130 cm of soil where it accumulates and increases soil acidity.